1. Field of the Invention refrigerant by controlling the flow rate of the refrigerant supplied to an evaporator in a refrigerating cycle, and according to the preamble part of claims 1 and 11.
In known expansion valves a valve body is arranged opposite to a valve seat formed by a thin contraction in the high-pressure refrigerant duct. Said valve body is moved in relation to said valve seat to open and close said valve seat corresponding to the temperature and the pressure of low-pressure refrigerant exiting the evaporator. The valve body is moved by an axially retractable rod which is guided along its shaft line in a penetration bore of the valve casing. Said rod is actuated by a power element operating corresponding to the temperature and the pressure of low-pressure refrigerant. In operation it may occur that due to some reasons the pressure of the high-pressure refrigerant supplied into the expansion valve significantly varies at the upstream side of the valve body. Said pressure variations are transmitted to the expansion valve body by means of the refrigerant medium. In case the pressure raises upstream the valve body due to a pressure variation, a pressure depending force acts on the valve body in its closing direction and consequently pushes said rod repeatedly. As a result, due to the closing or increasing throttling effect of the valve body the pressure of the refrigerants on the upstream side also is increasing and the occurring pressure variation even is multiplied. This might lead to an extremely unstable operation of the expansion valve.
2. Description of the Related Art
As disclosed in JP H 9-222 268 the operation of a known expansion valve was made stable by applying energy in lateral direction to the rod axially retractably disposed between the power element and the valve body, e.g. by a spring or the like. As a result, the valve body cannot respond as sensitively anymore to a variation of the pressure. However, the spring laterally pressing against the rod had to be made passive during a stable operation of the expansion valve and only should be set into action to stabilise the operation behaviour in case of pressure variations of the high-pressure refrigerant. As a result, the structure of the expansion valve became complicated as well as the assembling work, and the costs for manufacturing and assembling the expansion valve were high.
It is an object of the invention to provide an expansion valve performing a stabilised operation even in case of variations of the pressure of the high-pressure refrigerant and having an extremely simple and low cost design.